MARRIAGE is the death of hope," Woody Allen once said. But not for everyone. In New York, where eligible men are few and far between, single women who endure long stretches of unwilled celibacy may resort to cheating with someone else's husband because it seems like the only hope - consequences be damned. In December, I slept with a married man - late 50s, attractive, smart and successful. He's been with his wife forever, a lifestyle to which he is completely wedded, one that I had no intention of jeopardizing. Any guilt I might have felt was further assuaged by...